does anyone know if an agm gel battery can be charged via a normal van battery as i thinking bout buying one but i currently charge my battery at the moment using via my van battery through a relay switch but not usre if i can charge and agm one in this way

Only if it is AGM and not Gel as gel are more voltage sensitive. To be fair though, if you are constantly charging the battery via a split charge relay, you will not really gain anything from using an AGM. They do have a far higher cycle count but constantly charging the battery will reduce this by 30-40%.

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Just realised it may seem like I have given you conflicting advice from my last response. If you want to go down this route of charging the battery this way, be sure that relay that you are using is a voltage sensitive one that will only put the power in when it needs it. Some split charge relays will constantly charge both batteries.